Manufacture of artificial silk and the like



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Patented Apr. 19, 1927.

UNITED STATES 1,625,562 PATENT OFFICE.

FREDERICK CARL NIEDERHAU 'SER AND ALFRED ERNEST SUNDERLAND, OF ROANOKE,

VIRGINIA, ASSIGNORS TO THE VISCOSE COMPANY, OF MARCUS HOOK, PENNSYL-VATNIA A CORPORATION OF PENNSYLVANIA.

MANUFACTURE OF ARTIFICIAL SILK AND THE LIKE.

No Drawing.

Our invention relates to an improvement in the process of manufacturingproducts such as artificial silk from a cellulosic solution, andparticularly from solutions of cellulose xanthate or viscose. The objectof our invention is to provide a setting bath with an ingredient whichnot only reduces the stringent action of'the usual acid constituent ofthe bath, but also has the effectof retarding crystallization of saltscarried from the bath by a set product so that subsequent steps in thetreatment of the latter may be carried out with greater latitude asregards time sequence, without impairing its quality or strength.

In the manufacture of products such as. artificial silkor the like-fromcellulose solutions, e. g. as cellulose xanthate or viscose, thesolution is introduced through suitable orifices into a so-calledsetting bath, which has the effect of converting the solution intoproducts such as filaments having a certain body and tensile strength.Filaments thus formed are commonly led from the setting bat-h tosuitable spinning apparatus, where a group of filaments is twistedtogether to form a thread which is thereafter subjected to subsequenttreatment to remove all'traces' pf the bath and leave a thread of purecelluose.

The setting bath for viscose solution comprises a mineral acid, such assulphuric acid, a salt such as sodium sulphate, and in some casesotheringredients such as zinc, etc. As the filament or strip emergesfrom the setting bath it carries with it certain of. the ingredients ofthe solution, e. g. the salt. If the filament be permitted to dry, or tostand for a sufiicient period to partially dry, the salt crystallizes,ruptures the filament walls, and thus weakens the product. It isnecessary therefore to wash out the salt romptly in order to maintainthe strength 0 thefilament. This requires a fairly rapid sequence ofoperations, which it is not always convenient or possible to complete intime to insure the best results. Moreover, the acid of the bath has amore or less stringent ac} tion on the cellulose and tends to weaken thefilament and to impair the feel or quality of the product.

We have now discovered that by adding to the setting bath a suitablesubstance or substances, the stringency of the acid action Applicationfiled November 9. 1920. Serial No. 422,783.

upon the filament may be reduced and the crystallization of the salt inthe product after its Withdrawal from the setting bath may be greatlyretarded, with the advantageous result that the subsequent steps of theprocess may be carried out with greater latitude as regards timesequence, and without deleterious efiect upon the product. In fact theproduct of our researches has proved to be of improved quality asregards not only tensile strength, but also flexibility, texture andsoftness to the touch.

Various substances have been found suitable for the purpose, such assoluble colloids or emulsoids, e. g. gelatine,'glue, gum acacie(tragacanth) gum dragon and agar agar. Particularly serviceable andeconomical are gelatine or glue. The proportions in which theingredients may be added is variable, but we have found that about 2% ofglue added to the usual bath produces excellent results. Thus, to asetting bath having the usual content of acid (say about 8 partssulphuric acid) and salt (say about 15 parts sodium sulphate) a smallquantity (say 2 parts) of glue is added to produce the desired result.This addition not only raises the specific gravity of the solution, butalso increases its viscosity.

The product from such a bath may be kept for several days withoutcrystalliza u tion of its contained salt or injury to its strength.Moreover, our experiments have disclosed that the stringent action ofthe acid in the bath is lessened, as borne out by the feel of thefilaments, and also bystrength tests. Furthermore, a desirable cementingaction results, that is to say, where a group of filaments emerging fromthe bathis spun into a twisted thread, which is subsequently reeled,while partially dry, there is less of the undesirable flufiing of thefibers on the reel, due to the fact that the glue serves to hold thefibers or filaments together during the subsequent treatment of the sameafter leaving the bath.

No difficulty is experienced in removing this ingredient from theproduct in the final washing steps to which the latter is subjected. Infact after the usual sulphiding operation not a trace is left in thethread.

Obviously, the proportions of the added ingredient to the usual settingelements of,

the bath may be varied, and wide latitude is possible in the choice ofingredients which will have the desired ell'ect.

\Ve therefore do not limit our invention to the substances mentioned,but claim as our invention 1. In the manufacture of cellulose productsfrom a cellulosic solution, a setting bath into which the solution isprojected and from which the set product is withdrawn, said bathcomprising a crystalline reagent and a soluble colloid serving tomaterially retard the crystallization of said reagent in the set productwithdrawn from the bath.

2. In the manufacture of cellulose prodducts from a cellulosic solution,a setting bath into which the solution is projected and from which theset product is withdrawn, said bath comprising a crystalline reagent andgelatinous material serving to material- 1y retard the crystallization01' said reagent in the set product withdrawn from the bath. I

3. In the manufacture of cellulose products from a cellulosic solution,a setting hath into which the solution is projected and from which theset product 'is withdrawn, said bath comprising a salt, an acid, and asoluble colloid.

4. In the manufacture of cellulose products from a cellulosic solution,a setting bath into which the solution is projected and said bathcomprising an acid reagent and a soluble colloid serving to reduce thestringent action of the acid upon the prodnot.

In testimony whereof we have signed our names to this specification.

FREDERICK CARL NIEDERHAUSER. ALFRED ERNEST SUNDERLAND.

